My partner is HIV + and I am negative. As soon as he was diagnosed, he initiated treatment and after one year ( probably earlier ) his VL is undetectable ( yupi ! ). Since we met, we have never practiced unprotected sex and had never had an incident. I get tested every 6 months and so far so good. He only performs unprotected oral sex on me ( Im a female ). Now my question... what does it exactly mean that for someone under treatment the probability of transmission is reduced by 96%? I have tried to understand the statement from a statistical point of view, and frankly I dont get my head around it. 1. Does this mean that out of 100 unprotected encounters with someone that is HIV+ under treatment, there is only a probability of 4% to get infected? 2. or that out of 100 protected encounters with someone that is HIV+ under treatment, there is only a probability of 4% to get infected?

Basically what I'm trying to find out is whether for a discordant couple like me using condoms correct and consistently every single time ( I also make always sure that there was no leakage ), there is any chances of contracting HIV. And if there is any, why would this be?

The terror I go through every time I get tested is something that is seriously affecting me and thus I need to exactly know what my risks are regardless of all the prevention means in place.

Response from Dr. Wohl

Great question!

Here is what the '96%' we talk about means:

In a large clinical trial of 1,763 couples where, like in your case, one was HIV+ and the other HIV-, there was a 96% reduced risk of HIV transmission when the HIV+ person was randomized to start HIV meds vs those who were randomized to not start these meds.

In hard numbers, of the 877 couples where the HIV+ person did NOT start HIV meds immediately, there were 27 transmissions. In contrast, among the 886 couples where the HIV+ partner was randomized to start HIV therapy at once, there was only 1 transmission.

This translates into a 96% reduced risk (1 divided by 27 = .04).

In real world terms this means that under the study conditions, treating the HIV+ partner resulted in almost complete elimination of risk of transmission FROM THE HIV+ PARTNER. Note, the 1 case in the treatment arm has been well studied and likely occurred before the viral load was fully suppressed. Also, there were other cases of transmission of HIV to the negative partner but these were found to be from a third party and not the HIV+ partner. Lastly, this study involved loads of support for med adherence.

It is hard to translate this finding into an absolute number for an individual couple. Given your partner has an undetectable HIV RNA level, and assuming he is adherent to his meds , and that you use condoms even for all but oral sex, you can feel pretty secure that you are well protected from acquiring HIV from him. If all remains the same and no accidents (condom breaks), I would not advocate such rigorous HIV testing on your part. Even with a condom accident, the study suggests you would have a very very very low risk of acquiring HIV from a partner on effective HIV meds.

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